Fence Picket Calculator
Work out even picket spacing across a fence run, how many posts and pickets to buy, and how much lumber the whole fence takes — for picket, privacy and ranch rail fences.
Why a fence never divides evenly
A fence is where the fencepost problem gets its name, and on this job it bites twice — in opposite directions.
At the posts. A 48 ft run divided at 8 ft gives six bays, and six bays need seven posts. One more than the number of bays, because there is a post at each end as well as one between every pair of bays. That is the classic fencepost problem, and it is the easy half.
At the pickets. Inside a bay the pickets run from post to post and butt against both of them, so thirteen pickets leave twelve gaps, not fourteen. Now the pickets are the fenceposts and the gaps are the bays, and the count runs the other way. Get that backwards and every bay comes out one picket wrong.
The second count is why you cannot have both the gap you asked for and a whole number of pickets. In a bay with a clear span of C inches:
- Clear span = (pickets × picket width) + ((pickets − 1) × gap)
Three of those four numbers are yours to choose; the fourth falls out of the arithmetic. Pick the picket width and the gap you want and the count has to land on a whole number, which it usually does not — so the gap is what gives. The calculator rounds the count and then tells you the gap you actually get, instead of pretending the two match.
It works in both directions. If you know the gap you want, it gives you the count and the real gap. If you know the count — because thirteen pickets is what looked right on the last fence you built — it gives you the gap that count produces.
Posts first, then pickets
Measure the run once, end to end, and let the calculator split it. Do not measure bay by bay, and do not try to force the bays to a round number of feet: a run of 47 ft 6 in at an 8 ft target does not give you five tidy bays with 7 ft 6 in left over, it gives you six equal bays that are each slightly under 8 ft. That is the right answer. A short bay at the far end is the one thing that looks wrong from the road.
Two rules for the posts themselves:
- Keep them 6 to 8 ft on centre. That is the range fence builders work in for a 4 × 4 post carrying a fence up to 6 ft tall. Wider than that the fence racks sideways under a leaning load and the rails sag between posts; tighter than that you are digging holes you do not need.
- Hang a gate off its own two posts. A gate gets swung, leaned on and slammed, and the post it hangs from takes all of it. Build the gate as its own bay between two heavier posts rather than hanging it off the run.
Then lay out one bay and repeat it. Because every bay is the same width and every bay takes the same number of pickets, the layout you work out for the first bay is the layout for all of them — and that repetition is what makes the finished fence look even.
Picket, privacy and shadowbox
The arithmetic is identical for all three. The picket width and the gap are what change.
| Style | Board width | Gap | What it does |
|---|---|---|---|
| Picket fence | 1 × 4 or 1 × 6 (3½ or 5½ in) | 1½–3 in | Open and traditional. You can see through it, which is usually the point |
| Privacy fence | 1 × 6 (5½ in) | ⅛–¼ in | A solid screen. The gap is only there to let the boards move |
| Shadowbox | 1 × 6 (5½ in) | ⅛–¼ in, alternating sides | Near solid from your side, open to the wind from theirs |
A privacy fence is the same calculation with a very small gap. At ⅛ in the boards are all but touching, so the count is decided almost entirely by the board width — which makes a privacy fence the easier of the two to lay out, because there is very little to round.
Ranch rail is not in the table because there are no pickets to space: you run two or three horizontal rails between posts and the layout is just the posts. If that is the fence you are building, read the post and bay figures off this page and ignore the picket ones.
Picket spacing chart for an 8 ft bay
A 4 × 4 post set at 8 ft on centre leaves 92½ in of clear space between the post faces. These are real outputs from the calculator for that bay with 1 × 6 pickets.
| Gap you ask for | Pickets per bay | Gap you get | How it reads |
|---|---|---|---|
| 1/8 in | 16 | 5/16 in | Privacy. The boards are all but touching |
| 1/2 in | 16 | 5/16 in | The same fence — the count did not change |
| 1 in | 14 | 1 3/16 in | Tight picket |
| 2 in | 13 | 1 3/4 in | Classic picket fence |
| 3 in | 11 | 3 3/16 in | Open picket |
| 4 in | 10 | 4 3/16 in | Between a picket fence and ranch rail |
| 5 in | 9 | 5 3/8 in | Very open — needs a low fence and a long run |
Two things worth noticing. Asking for ⅛ in and asking for ½ in give you exactly the same fence, because both land on sixteen pickets — the count is what you are really choosing, and the gap is a symptom of it. And the gap moves in bigger absolute steps as the count falls: one picket either way at sixteen shifts the gap by less than half an inch, while one picket either way at ten shifts it by the better part of an inch.
Worked example: a 48 ft run
Take a 48 ft run, 4 × 4 posts at 8 ft on centre, 1 × 6 pickets, a 2 in gap, a 72 in fence and 10% waste.
The run splits into 6 equal bays of 8 ft, so 7 posts. Each bay is 96 in between post centres; take off the 3½ in post and you have 92½ in of clear space.
Thirteen pickets at 5½ in is 71½ in. That leaves 21 in to share between the twelve gaps, so the gap is 1¾ in — a shade under the 2 in you asked for, and the same in every bay.
For material: 13 pickets × 6 bays is 78 pickets at 72 in each, or 468 linear ft. Rails are two per bay at 96 in, so 12 rails, or 96 linear ft. Posts are 7 at 96 in — 72 in above ground plus 24 in buried — which is 56 linear ft. That is 620 linear ft, and 10% waste brings it to 682 linear ft, or 86 boards of 8 ft.
Check one thing before you order. Fence pickets are usually sold pre-cut at 6 ft, so if you buy them that way the 8 ft board count only covers the rails and the posts — 152 linear ft, which is 21 boards with the waste allowed for. Buy the pickets as pickets and the boards as boards, and this page's arithmetic splits the same way.
Does the building code cover fences?
No. The International Residential Code does not regulate a garden, picket or privacy fence. There is no code figure for picket width, gap, post spacing or fence height. Height, setback and which side faces out are zoning, set by your city or county, and they change from one street to the next — so everything on this page is arithmetic and trade practice, not law.
Read the ordinance before you dig, not after. A fence over the height limit is the kind of thing a neighbour can make you take down, and a post that has already been set in concrete is a day of work to move.
There is one exception worth knowing, because it is where people assume the ordinary rules apply and they do not. A fence that encloses a swimming pool is a pool barrier, and that is a regulated assembly with its own limits on height and on the openings a small child could pass through. Treating a pool fence as a taller version of this one is how a fence fails an inspection it was never going to pass. If there is water on the property, look up the pool barrier rules for your area before you lay anything out.
For the layout itself, three things decide the result, and only two of them are numbers you measure:
- The run. Measure it once, end to end, along the line the posts will actually sit on — not along the house.
- The actual board width. A 1 × 6 is 5½ in, not 6. Using the nominal size in an 8 ft bay throws the count out by a whole picket.
- The count you want. Decide the number of pickets per bay first and let the gap fall where it falls. Choosing a gap and hoping the count comes out whole is the mistake this page exists to prevent.
Frequently asked questions
How do I space fence pickets evenly?
Work per bay, not across the whole run. Take the distance between two post centres, subtract the post width to get the clear span, then decide how many pickets you want in that span. The pickets butt against both posts, so the number of gaps is one less than the number of pickets — 13 pickets leave 12 gaps. Divide whatever is left after the pickets by that gap count and you have your spacing. Every bay gets the same layout, so you only work it out once.
How many pickets do I need for a 48 ft fence?
With 4 × 4 posts at 8 ft on centre you get 6 bays and 7 posts. In each bay, 1 × 6 pickets at a 2 in gap come out at 13 pickets, so 78 pickets for the run. Narrower pickets push the count up fast: 1 × 4 pickets in the same bay come out at 17 each, which is 102 pickets on the same run — about 30% more lumber for the same length of fence.
What gap should I leave between pickets?
It is a look, not a rule. A classic picket fence runs 1½–3 in; a privacy fence runs ⅛–¼ in, where the gap exists only to let the boards move as they take on water and dry out. Above about 6 in it stops reading as a picket fence and starts reading as ranch rail. The one gap worth avoiding is none at all: boards that are butted tight against each other have nowhere to go when they swell, and they will cup, split, or push the rails off the posts.
How far apart should fence posts be?
Six to eight feet on centre for a 4 × 4 post carrying a fence up to 6 ft tall. That is the range fence builders work in, and it is a trade convention rather than a code figure. Wider than that the fence racks sideways under a leaning load and the rails sag between posts; a 6 × 6 post buys back some of that, but not all of it. Whichever you pick, divide the run into equal bays — that matters more to how the fence looks than the exact spacing does.
How deep should fence posts be set?
Below the frost line, which is a local number — nothing at all on the Gulf coast, 48 in or more across the northern Plains and New England. Your building department publishes it. The reason is heave: a post set above the frost line gets lifted by the ground freezing and thawing under it, and no amount of concrete stops that, because the whole footing moves with the soil. As a starting point, 24 in below grade is enough in a mild climate and nowhere near enough where the ground freezes hard.
Is a 1 × 6 actually 6 inches wide?
No. A 1 × 6 is 5½ in wide, a 1 × 4 is 3½ in and a 1 × 8 is 7¼ in, because the board is planed after it is sawn. This matters more in a fence than almost anywhere else, because the picket width is the biggest single number in the layout: entering 6 in instead of 5½ in in an 8 ft bay drops you from 13 pickets to 12, which is 6 fewer pickets over a 48 ft run. Measure the boards you were actually sold.
What do I do where the ground slopes?
Step the fence rather than rack it. Racking — tilting every picket so the top edge follows the slope — looks tidy on a gentle grade and looks wrong on anything steep, because the pickets stop being vertical and the eye reads it immediately. Stepping keeps every picket vertical and every panel square: run the fence level for a bay or two, then drop the next section by a whole picket length or half of one. The layout per bay does not change; only the post heights and the picket lengths at the step do.
How much lumber do I need for a fence?
Three parts. Pickets: the number per bay times the number of bays, each one fence height. Rails: two per bay, each one bay width. Posts: one more than the number of bays, each post the fence height plus the buried length. On a 48 ft run with 1 × 6 pickets, an 8 ft post spacing, a 72 in fence and posts buried 24 in, that comes to 468 linear ft of pickets, 96 of rails and 56 of posts — 620 linear ft, or 682 with 10% waste. Pickets are usually sold pre-cut at 6 ft, so if you buy them that way the board count only covers the rails and the posts.